If zoom is important,I guess it has to be the SX40hs- if low light use is important,the S100 would lead(just)- though I personally might go for the more "robust" G12...
Another great "all rounder" is the versatile Panasonic FZ-150.
Great pic quality is subjective- though all of the above are pretty much leaders in their class....

camdevil- all of the above have their strong points- it comes down to which you value most in a camera. Which is most important? Pocketability/size? Zoom range? Low light capability..? Build quality...?
What are you most likely to be shooting frequently...?
And if you're considering the G12- maybe also look at Nikon's P7100...

The only thing I WILL say is that I think the S100 is better on many counts than the S95.
The SX40hs(which I have) is a very versatile camera- and a great all rounder,though is quite a different camera to the G12. If video is important then it's the SX40 all the way- shooting full HD- plus a variety of other resolutions- and unlike the G12- you can use the optical zoom whilst filming. The G12 is a very well built picture taker,with good old fashioned dials for old school photographers- but that's about it..! In many regards- the S100 is a more versatile camera than the G12- having a faster(wider)aperture to aid in low light and HD video WITH optical zoom and is more pocketable.
I guess you pay for the G12's build quality...!

On the face of it,they're both very similar- that being a well built compact(ish..!) camera for someone who wants to indulge in a bit more than just snapping in Auto mode...
On paper the Nikon outdoes the Canon simply by having a better video mode with which you can use the optical zoom- and the 7x zoom is clearly an advantage over the Canon's 5x zoom. On image quality I think the Canon edges it- just- but I'm talking really small differences here- barely noticeable- and that is only at higher iso settings(800 and 1600) where the G12 seems to be just a little bit cleaner.
A couple of reviews....